Many kind of silver halide color photographic materials and methods of forming color images are commercially available at the present time. Various improvements and inventions thereon have been made depending on the end use.
The formation of color photographic images by the image-wise coupling of oxidized primary aromatic amino developing agents with color forming or coupling compounds to form indoaniline, indophenol, and azomethine dyes is well known. In these processes, the subtractive process of color formation is ordinarily used, and the image dyes customarily formed are cyan, magenta, and yellow, the colors that are complementary to the primary colors, red, green, and blue, respectively. Usually phenol or naphthol couplers are used to form the cyan dye image; pyrazolone or cyanoacetyl couplers are used to form the magenta dye image; and acylacetamide couplers are used to form the yellow dye image.
In these color photographic systems, the color-forming coupler may be either in the developer solution or incorporated in the light-sensitive photographic emulsion layer so that, during development, it is available in the emulsion layer to react with the color development agent that is oxidized by silver image development. Diffusible couplers are used in color developer solutions. Nondiffusible couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are selected which form non-diffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
It is generally desired that silver halide emulsion employed in these color photographic materials have high sensitivity. Therefore, silver iodobromide, silver chloroiodobromide or silver chlorobromide (each being mainly constituted of silver bromide) are generally used as the silver halide in the emulsions.
Silver halides mainly composed of silver bromide (i.e., at least 50% by molarity of anions) are theoretically disadvantageous for the purpose of rapid processing because the bromide ions which are released from the silver halides when they are developed have a development inhibiting function. From the standpoint of rapid processing, it is preferred to employ silver halides mainly composed of silver chloride. However, it is known that silver halide compositions mainly composed of silver chloride have some disadvantages in that they are apt to fog, particularly when they have a high development speed. They also tend to have poor preservation stability and have low sensitivity.
Because of the disadvantages described above, it is difficult for silver halides mainly composed of silver chloride to be exploited for their excellent developability in methods of forming image having relatively high sensitivity.
Various kinds of development accelerators have been investigated in order to increase the color forming property and to shorten the processing time in color development during processing of color photographic material. Particularly, benzyl alcohol is widely employed at present in this manner.
Increasingly, however, reduction of development processing time, simplification of the processing system and operation, and achievement of low environmental pollution are required of photographic products, in addition to high sensitivity.
These requirements are being made because reduction of the development period, simplification of laboratory work, improvement in miniaturization, and simple operation of the processing system for small scale laboratories are desired. With respect to said requirements, benzyl alcohol which is used in the color developing solution causes severe problems.
Since benzyl alcohol has a low water solubility, it is necessary to use solvents such as diethylene glycol in order to assist in dissolution of the benzyl alcohol. These compounds, including the benzyl alcohol, exhibit a large value of BOD (biological oxygen demand) and COD (chemical oxygen demand) which indicate a large load for prevention of environmental pollution. Therefore, it is desirable to eliminate these compounds to simplify protection of the environment. Also, it takes much time to dissolve benzyl alcohol in a developing solution even when a solvent is employed and, thus, it is desirable to eliminate benzyl alcohol to simplify work for the preparation of the developing solution. However, to simply eliminate benzyl alcohol results in a severe slowing of color development which is contrary to the needs of rapid processing in the market. Thus, it has been desired to develop a substitute for the use of benzyl alcohol.
Photographic color developing compositions used heretofore have typically been adapted for use with high bromide silver halide photographic elements. These conventional developing compositions tend to give less than satisfactory results.
For example, they typically contain restraining agents such as potassium bromide, which exert too great a retardation effect on development for obtaining a high value of D.max. Moreover, they typically contain hydroxylamine, or a water-soluble acid salt thereof, which functions as an antioxidant and thereby serves to protect the primary aromatic amino color developing agent against oxidation. Use of hydroxylamine, or a water-soluble acid salt thereof, is disadvantageous, however, since it tends to act as a scavenger which inactivates oxidized color developing agent before it can react with coupler to form dye. It can also act as a developing agent which competes with the color developing agent unless it is adequately restrained by bromide. In addition to hydroxylamine or a water-soluble acid salt thereof, developing solutions heretofore used with high bromide silver halide elements often contain substantial concentrations of sulfite to also provide protection against oxidation of the developing agent. The sulfite, which is typically utilized in the form of an alkali metal sulfite or bisulfite, functions to sulfonate oxidized color developing agent and, when used in sufficient concentration, its competition with coupler for oxidized color developing agent seriously affects dye formation.
In light of the above, it is clear that there is a need in the art to provide photographic color developing compositions useful to developing high bromide silver halide elements that reduce the problems heretofore mentioned.